Function join_read_const_table

sql/sql_select.cc:25129–25240

*/

static int
join_read_const_table(THD *thd, JOIN_TAB *tab, POSITION *pos)
{
  int error;
  TABLE_LIST *tbl;
  DBUG_ENTER("join_read_const_table");
  TABLE *table=tab->table;
  table->const_table=1;
  table->null_row=0;
  table->status=STATUS_NO_RECORD;
  
  if (tab->table->pos_in_table_list->is_materialized_derived() &&
      !tab->table->pos_in_table_list->fill_me)
  {
    DBUG_ASSERT(0);
    //TODO: don't get here at all
    /*
      Skip materialized derived tables/views as they temporary table is not
      opened yet.
    */
    DBUG_RETURN(0);
  }
  else if (tab->table->pos_in_table_list->jtbm_subselect &&
           tab->table->pos_in_table_list->jtbm_subselect->is_jtbm_const_tab)
  {
    /* Row will not be found */
    int res;
    if (tab->table->pos_in_table_list->jtbm_subselect->jtbm_const_row_found)
      res= 0;
    else
      res= -1;
    DBUG_RETURN(res);
  }
  else if (tab->type == JT_SYSTEM)
  {
    if (unlikely((error=join_read_system(tab))))
    {						// Info for DESCRIBE
      tab->info= ET_CONST_ROW_NOT_FOUND;
      /* Mark for EXPLAIN that the row was not found */
      pos->records_read= pos->records_out= 0.0;
      pos->ref_depend_map= 0;
      if (!table->pos_in_table_list->outer_join || error > 0)
	DBUG_RETURN(error);
    }
    /*
      The optimizer trust the engine that when stats.records is 0, there
      was no found rows
    */
    DBUG_ASSERT(table->file->stats.records > 0 || error);
  }
  else
  {
    error=join_read_const(tab);
    if (unlikely(error))
    {
      tab->info= ET_UNIQUE_ROW_NOT_FOUND;
      /* Mark for EXPLAIN that the row was not found */
      pos->records_read= pos->records_out= 0.0;